This invention generally relates to an apparatus for plugging wells and more specifically to a barrier which can be lowered into a well on a pipe string and which will support a column of plugging fluid.
As is well known, it is often necessary to plug various types of wells. Such wells may consist of, but are not limited to, oil and gas wells, disposal wells and injection wells used for subterranean storage. These are merely examples and as is well known other types of wells must also be plugged for a variety of reasons. One common problem when plugging wells is achieving a positive bottom barrier. Very often, the well to be plugged cannot support a column of plugging fluids, such as a cement slurry.
Generally, a well is plugged by displacing a plugging fluid which can be a cement mixture or any other plugging fluid known in the art, to a supply pipe at a location where the plug is to be set. Generally, before the cement mixture or other plugging fluid is added, the well will have a fluid, such as drilling fluid therein, and the cement or other plugging fluid is carried by the drilling fluid until the cement mixture hardens. There are a number of difficulties associated with setting plugs in this manner. The plugging fluid may become mixed or contaminated with the fluid in the well, which can damage the integrity of the plugging fluid such that sufficient hardness is not reached. There are other times when plugs set in this manner end up lower than desired because the plugging fluid settles to a position lower in the wellbore than the desired plug location. Furthermore, there are times when the plug does not adequately fill the well at the plug location such that it may have a tendency to slip and/or tilt in the well.
Certain of these difficulties are addressed in U.S. Pat. No. 5,667,015 which discloses a well barrier. The barrier shown therein, however, is still susceptible to moving within a wellbore so that the plug may ultimately not be located at the desired plug location.
Thus there is a need for an apparatus and method for providing a positive bottom barrier so that the well can be effectively plugged. The barrier must be capable of supporting the hydrostatic weight of upper fluid columns that may consist of drilling muds, brines and cement slurries, and more specifically should be able to support the hydrostatic weight of a column of hydraulic cement or other plugging fluid or material. When such fluids harden, or develop substantial gel strength, the fluids are self-supporting in the well. The present invention overcomes the above-mentioned problems by providing a positive bottom barrier in an economical and time-efficient manner.
The present invention provides a method and apparatus for plugging a well. The apparatus comprises a support pipe defining a central flow passage and has a plurality of openings which intersect the central flow passage. A fluid barrier is attached to the support pipe below the plurality of openings. The fluid barrier will catch a plugging fluid displaced through the flow passage and communicated through the openings in the support pipe.
The fluid barrier may comprise a canvas material and may include a plurality of support members for supporting the canvas material. The support members may be hingedly connected to the support pipe. Thus, the fluid barrier may be movable and may be moved from a closed position when it is being lowered into a well to an open position at a selected plug location in the well.
The fluid barrier has a central opening through which the support pipe is received. Thus, the barrier is disposed about the support pipe and extends radially outwardly therefrom. Thus, in its open position the fluid barrier comprises an upwardly opening barrier that extends radially outwardly from the support pipe and will engage the well at the selected plug location. The apparatus includes a means for preventing the barrier from opening past a fully open position and also includes a means for maintaining the barrier in its open position at the selected plug location.
The support pipe may be connected to and lowered into a well by any means known in the art but is preferably lowered with tubing, jointed pipe or other string of pipe known in the art. The string of pipe is connected to the support pipe, and the central flow passage of the support pipe is communicated with a central opening or central flow passage of the string of pipe thereabove. Once the plugging apparatus has been lowered to the selected plug location in the well, the plugging fluid can be displaced through the string of pipe and into the support pipe. The plugging fluid will exit the support pipe through the openings therein above the fluid barrier. The fluid barrier will catch the plugging fluid that exits the support pipe. Once a sufficient amount of plugging fluid has been displaced into the well, the plugging fluid is allowed to harden or gel sufficiently such that it will support its own weight in the well. Once this occurs, the string of pipe utilized to lower the apparatus into the well is removed therefrom. The string of pipe may be removed by utilizing a chemical cutting tool or by utilizing a shear activated coupling device to attach the string of pipe to the support pipe to allow the string of pipe to be removed.
Further objects, features and advantages of the present invention will be understood from the following description when read in conjunction with the accompanying drawings.